Connectivity fault management in a communication network

ABSTRACT

Methods and apparatus are disclosed for monitoring a Maintenance Association (MA) for Connectivity Fault Management (CFM) in a network supporting Equal Cost Multiple Paths (ECMP). A set of ECMP paths is generated for sending data between endpoints in the network. Furthermore, a set of ECMP MAs is created that are used for monitoring the generated ECMP paths between the endpoints. The created set of ECMP MAs is subsequently used for sending monitoring packets. ECMP path MAs therefore conform to existing CFM operation and are compatible with both ECMP point to point path MAs and ECMP multipoint path MAs.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/414,338, filed Jan. 12, 2015, which is a 371 of InternationalApplication No. PCT/EP2013/064785, filed Jul. 12, 2013, which claims thebenefit of U.S. Provisional Application No. 61/671,343, filed Jul. 13,2012, the disclosures of which are fully incorporated herein byreference.

TECHNICAL FIELD

The invention relates to the field of Connectivity Fault Management in acommunications network, in particular a network that supports Equal CostMultiple Paths.

BACKGROUND

Operations, Administration and Maintenance (OAM) is a term used todescribe processes, activities, tools, standards and so on that areinvolved with operating, administering, managing and maintaining acommunication network. OAM requires fault management and performancemonitoring, connectivity fault management and link layer discovery.

CFM is a protocol of OAM that provides Connectivity Fault Management(CFM). The CFM protocol uses Maintenance Domains (MD) for monitoringlevels of service providers, core networks or system operators. Eachlevel has Maintenance Associations (MA) dedicated to monitoring specificprovider/provider or provider/customer service. Each MA depends on a setof Maintenance Points (MPs) for monitoring. An MA is established toverify the integrity of a single service instance. A MaintenanceAssociation Edge Point (MEP) is an actively managed CFM entity whichprovides the extent of an MA and is associated with a specific port of aservice instance. It can generate and receive CFM Protocol Data Units(PDUs) and track any responses. It is an end point of a single MA, andis an endpoint for each of the other MEPs in the same MA.

CFM PDUs are transmitted by a MEP in order to monitor the service towhich the transmitting MEP belongs. A problem arises in Equal-CostMultiple Paths routing (ECMP) networks where CFMs cannot be guaranteedto take the same path as the data.

ECMP routing is a forwarding mechanism for routing packets alongmultiple paths of equal cost. An aim of ECMP is to equalise distributedlink load sharing. Referring to FIG. 1, there is illustratedschematically a very simple network architecture in which data sentbetween two endpoints 1, 2 can be sent via intermediate nodes 3 or 4 atequal cost. Some data packets are sent via intermediate node 3 andothers are sent via intermediate node 4. In this way the load on thenetwork is balanced.

Shortest Path Bridging (SPB) enables the use of link state protocols(IS-IS) for constructing active topologies within a Bridged Network. Formore information, see IEEE Std 802.1aq-2012, Shortest Path Bridging.Recent standardization work within IEEE802.1 enhances SPB by enablingECMP support on SPBM services that use the same VID identifier, asdescribed in P802.1Qbp/D1.0 Equal Cost Multiple Path (ECMP). P802.1Qbpdiscusses the services supporting ECMP connectivity and, in particular,defines two types of ECMP connectivity. One is associated withpoint-to-point (PtP) ECMP services provided by ECMP devices that supportflow filtering. The other is a generic Virtual LAN (VLAN) serviceassociated with a specific VLAN Identifier (VID) that is mapped to ECMPoperation (SPBM VLAN MA in clause 27.18.1 in P802.1Qbp/D1.0 Equal CostMultiple Path).

ECMP connectivity paths may use the same Bridging VLAN Identifier(B-VID) in their tags but the service connectivity provided by thesepaths are different than that associated with frames having the sameB-VID and controlled by traditional L2 control protocols like spanningtree or SPB . A typical example of connectivity instances that use thesame VID but are not members of a VLAN are Traffic Engineered ServiceInstances (TESIs) in Provider Backbone Bridges-Traffic Engineering(PBB-TE). ECMP connectivity is similar to that of TESIs but it has afurther property that a superset of all ECMP paths identified by thesame VID (and endpoints) is not a tree topology. A VLAN on the otherhand is always defined in a context of a tree (see clause 7 in IEEE Std802.1Q-2011, VLAN aware Bridges).

Shortest Path Bridging—MAC address mode (SPBM) connectivity is differentto ECMP connectivity. SPBM connectivity is similar to that of PBB-TE (inthat it there is no flooding, no learning, it is symmetric, and usesonly explicit entries in a Filtering Database (FDB) for forwarding),which means in practice that CFM enhancements for PBB-TE (described inIEEE Std 802.1Qay-2009 PBB-TE and IEEE Std 802.1Q-2011, VLAN awareBridges) can be used almost identically for SPBM MAs. Nevertheless, ECMPconnectivity differs in that multiple paths are enabled for the same endpoints. The same VID and correspondingly the ECMP CFM require furtherchanges in order to monitor the associated services. As a result ECMPMAs need to be separated from SPBM MAs, and the associated monitoringprotocol tools need to be modified as their operation depends on thetype of connectivity that they monitor.

ECMP Point-to-Point (PtP) path connectivity and the associatedmonitoring tools are described in P802.1Qbp, but P802.1Qbp does notdescribe ECMP multipoint monitoring in a consistent manner. Inparticular, the “SPBM VLAN” connectivity is associated with an overallconnectivity identified by the same SPBM VID value. However, an overallSPBM-VID connectivity is meaningless for ECMP, because ECMP createsmultiple independent connectivity paths between subsets of nodes thatare members of the SPBM-VID. The operational status of each of the ECMPsubsets is therefore independent of the operational status of the otherECMP subsets identified by the same SPBM-VID. This ECMP independencymeans that, when using SPBM OAM mechanisms and an overall SPBM-VIDconnectivity is reported as being error-free, the connectivity on ECMPsubsets could be non-operational. The above connectivity characteristicof the SPBM VLAN Maintenance Association (MA) creates problems formonitoring multipoint ECMP services. In particular, since the SPBM VLANContinuity Check protocol attempts to monitor the overall “VLAN”service, the scope of propagation of the Continuity Check Message (CCM)PDUs is provided by the use of a broadcast address (constructed usingSPBM default Backbone Service Identifier, I-SID). The result of this isthat monitored connectivity is different from the connectivityassociated with the monitored data traffic. In addition, the operationof Link Trace Messages (LTM) becomes quite difficult and the extent ofreachability of the LTMs can be quite different to that defined by theconfigured ECMP related MAC address entries.

Furthermore, the placement of the “SPBM VLAN MEP” in parallel to ECMPPtP path Maintenance Association Edge Points (MEPs) breaks the operationof the ECMP path MAs (stopping every ECMP Path CFM PDU on the SPBM-VIDas can be seen from FIG. 27-4 in P802.1Qbp/D1.0.)

SUMMARY

It is an object to provide a mechanism by which Connectivity FaultManagement Maintenance Associations can be monitored in an Equal CostMultiple Paths network.

According to a first aspect, there is provided a method of monitoring aMaintenance Association (MA) for Connectivity Fault Management (CFM) ina network supporting Equal Cost Multiple Paths (ECMP). A set of ECMPpaths is generated for sending data between endpoints in the network.Furthermore, a set of ECMP MAs is created that are used for monitoringthe generated ECMP paths between the endpoints. The created set of ECMPMAs is subsequently used for sending monitoring packets. An advantage ofthis is that ECMP paths MAs conform to existing CFM operation and arecompatible with both ECMP point to point path MAs and ECMP multipointpath MAs.

As an option, each monitoring packet comprises a CFM Protocol Data Unit.An advantage is that the forwarding parameters of the PDU are the sameas those for monitored data packets sent using the ECMP paths, and sothe monitoring packets will traverse the same path.

As an option, the method includes generating the set of ECMP paths usingECMP Point to Point paths, wherein the Point to Point paths comprising aset of equal shortest length connectivity paths between the two endpoints.

As an alternative option, the method includes generating the set of ECMPpaths using ECMP multipoint paths. The multipoint paths include a set ofconnectivity multipoint paths among the same end points. As a furtheroption, each ECMP path comprises an ECMP multipoint path having Nendpoints. Each ECMP multipoint path may be identified using a Groupaddress. As a further option, each ECMP multipoint path associated withthe two end points may be identified using a Group MAC address. In thiscase, the Group MAC address is optionally constructed by applying anoperation on Backbone Service Identifier values associated with the ECMPmultipoint paths.

As an option, the method further includes monitoring an ECMP path bysending the monitored packet using the identifier associated with thespecific path. Optional examples of such an identifier are a Flow Hashand a Group MAC address identifying the path.

As an alternative option, the method further includes monitoring aplurality of ECMP paths by sending monitored packets in groupscyclically on each monitored ECMP path, using the identifier associatedwith each monitored ECMP path.

According to a second aspect, there is provided a node for use in acommunications network supporting ECMP. The node is provided with aprocessor for generating a set of ECMP path MAs for sending data betweenend points. The processor is further arranged to create a set of ECMPMAs for monitoring the generated ECMP paths between the endpoints. Atransmitter is also provided for sending monitoring packets using theset of generated ECMP paths. An advantage of this is that ECMP paths MAsconform to existing CFM operations, and are compatible with both ECMPpoint to point path MAs and ECMP multipoint path MAs. The node isoptionally implemented in any type of device that implements ECMP.

As an option, the node is provided with a computer readable medium inthe form of a memory for storing information mapping at least oneService Identifier to each generated ECMP path.

The processor is optionally arranged to generate monitoring packetsusing ECMP Point to Point paths comprising a set of equal shortestlength connectivity paths between the end points.

As an alternative option, the processor is arranged to generatemonitoring packets using ECMP multipoint paths comprising a set ofconnectivity multipoint paths among a plurality of end points. As afurther option, the processor is arranged to identify an ECMP multipointpath monitoring packet using a Group MAC address for each ECMP path. Inthis case, the processor is optionally arranged to construct each GroupMAC address by applying an operation on Backbone Service Identifiervalues associated with the ECMP multipoint paths.

According to a third aspect, there is provided a computer programcomprising computer readable code which, when run on a node, causes thenode to perform the method as described above in the first aspect.

According to a fourth aspect, there is provided a computer programproduct comprising a non-transitory computer readable medium and acomputer program described above in the third aspect, wherein thecomputer program is stored on the computer readable medium.

According to a fifth aspect, there is provided a vessel or vehiclecomprising the node described above in the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically in a block diagram a networkarchitecture showing the principles of Equal Cost Multiple Path routing:

FIG. 2 is a flow diagram showing steps according to an embodiment;

FIG. 3 illustrates schematically in a block diagram an exemplary node;and

FIG. 4 illustrates schematically in a block diagram an exemplary vesselor vehicle.

DETAILED DESCRIPTION

A consistent way of enabling OAM monitoring for Connectivity FaultManagement for both ECMP PtP path MAs and ECMP Multipoint path MAs isprovided. “Fate sharing” is guaranteed by using the same forwardingparameters for monitoring packets such as CFM PDUs monitoring the ECMPservice as for monitored data frames. In particular, the destinationaddress of CFM PDUs associated with ECMP path MAs is the same addressused to reach remote MEPs within the same MA, and is provided by theconfiguration of the MA itself. Each specific ECMP is identified by aFlow Hash value and any subsets of ECMP paths within the same PtP pathare identified by the associated subset of Flow Hash values.

An ECMP path MA is associated with a connectivity path connecting aspecific group of endpoints or with a subset (not necessarily proper) ofequal cost paths connecting the same end points. In the latter case, thecorresponding CFM PDUs are sent in groups cyclically on every monitoredpath, using an identifier associated with every monitored path. Thenumber of CFM PDUs in every group depends on the specific CFM PDU: Forexample, for CCMs, at least four CCMs must be sent on a single monitoredpath before moving to the next one. For Loopback Messages (LBMs), asmany LBMs as provided by the administrator that initiates the LBM aresent. Only one LTM need be sent. This is because CCMs are sentperiodically, and a fault is only reported when more than threeconsecutive CCMs are in error (so we need to send at least four on thesame path to be able to check it). The periodicity of LBMs (if any) isconfigurable and correspondingly the number of LBMs on individual pathsmust be based on the configuration setting. LTMs are set to identifyindividual nodes along the path, and so only one LTM on each individualpath is required.

In the case of ECMP multipoint path services, the destination_addressparameter of the associated monitoring CFM PDUs is set cyclically to theSPBM Group MAC address associated with the monitored multipoint service.SPBM Group MAC address assignment can be automated.

In more detail, two ECMP connectivity paths are defined as follows:

1. ECMP PtP path: This is the complete set of equal shortest lengthconnectivity paths between two specific end points as constructed byECMP. In addition to what is described in P802.1Qbp/1.0, LB and LT usethe same cyclic methods when a subset of Flow Hash values is provided.

2. ECMP multipoint path: This is the complete set of connectivitymultipoint paths among more than two end points as constructed by ECMP.A single multipoint path within an ECMP multipoint path of N endpointsis identified either by:

(a). N Group MAC addresses constructed as follows: the first 3 bytescorresponding to the SPsourceID of the initiating Backbone Edge Bridge(BEB) and the last 3 bytes corresponding to the same I-SID identifyingthe N endpoint connectivity (this I-SID value may be automated to, forexample, be the least backbone I-SID value on the set of I-SID valuesmapped to an ECMP-VID operation within the Backbone Service Instancetable on the terminating BEBs having the least SPsourceID), that is:(SPsourceID[1]-ISID, SPsourceID[2]-ISID, . . . , SPsourceID[N]-ISID); or(b). A single Group MAC address for all endpoints constructed asfollows: the first 3 bytes corresponding to the IEEE 802.1Q BackboneService Instance Group address OUI (see clause 26.4 in IEEE Std802.1Q-2011, VLAN aware Bridges) and the last three bytes correspondingto the same I-SID identifying the N endpoint connectivity (this I-SIDvalue chosen could be automated to, for example, be the least backboneI-SID value on the set of I-SID values mapped to an ECMP-VID operationwithin the Backbone Service Instance table on the terminating BEBshaving the least SPsourceID). That is the same group address that isused for all I-SID endpoints corresponding to the Backbone Serviceinstance Group Address.

The choice between (a) and (b) type of addressing described above ismade by configuration. Note that the selection of (a) or (b) depends onhow the ECMP multipoint connectivity is set up. Option (a) requires theset up N individual MAC addresses for an N point connectivity, whileoption (b) requires a single MAC address for an N-point connectivity.Option (a) provides better coverage at the expense of increasedcomplexity.

Other multipoint paths (up to 16 for each group, a or b) within the sameECMP multipoint connectivity associated with exactly the same Nendpoints can be identified by using Group MAC addresses constructed bythe above sets by x:oring the I-SID values in (a) or (b) type addressingusing tie break masks described in 28.8 in IEEE Std 802.1aq-2012,Shortest Path Bridging.

In order to enable ECMP operation, an I-SID to path mapping table mustbe configured for all local I-SIDs that map to the B-VID indicating ECMPoperation on the BEBs Backbone Service Instance table. Note that theremay be a default configuration set to distribute I-SIDs equally to allECMP paths. In this case, I-SIDs can be mapped in increasing order topaths. Table 1 below is an example of such a table:

TABLE 1 Exemplary mapping of I-SIDs to paths. I-SID₁, I-SID₂, . . . ,I-SID_(k) Path 1 I-SID_(k+1), . . . , I-SID_(k+m) Path 2 I-SID_(p), . .. , I-SID_(z) Path 16

For each subset of I-SID values that are mapped on the same path, theleast I-SID_(low) value is identified and all the subsets are ordered onincreasing I-SID_(low) values. The I-SID subsets are then mapped tomultipoint paths identified by Group MAC addresses constructed asdefined above and x:ored in accordance with IEEE std 802.1aq-2012 inincreasing order. Table 2 illustrates an I-SID distribution table whenaddressing method (a) is used:

TABLE 2 Exemplary mapping of I-SIDs to paths 1000, 40000, 3443 Path 1  999, 104000 Path 2 39000, 1010 Path 3 800000, 995  Path 4

An exemplary automated constructed Group MAC for a node identified bySPSourceID 5 (having the appropriate multicast address bit set) is shownin Table 3.

TABLE 3 Exemplary automated constructed Group MAC 800000, 995  5-995  999, 104000 5-(995 x:ored 0x01) 1000, 40000, 3443 5-(995 x:ored 0x02)39000, 1010 5-(995 x:ored 0x03)

The method described above provides a way to automate the allocation ofidentifiers of individual paths within ECMP multipoint pathconnectivity.

The address used by CFM PDUs to reach remote MEPs within the same ECMPpath MA is provided by the configuration of the MA itself. In the caseof the ECMP multipoint path MAs it is an SPBM Group Address associatedwith the monitored service. The above method describes a way to automatethe distribution of Group addresses based on the I-SID ECMPconfiguration tables. In the case of a single path with the ECMP pathMA, the CFM PDUs use the MAC address associated with it. In cases wheremore then one path is monitored, the CFM PDUs are cyclically destined tothe associated Group MAC addresses.

The associated ECMP path MEPs are placed on a Customer Backbone Port(CBP) by using the TESI multiplex entities and using the associatedGroup MAC address identifiers

The techniques described above enable automated configuration of ECMPmultipoint path MAs in a way that does not require alterations toexisting CFM operations, and is compatible with ECMP PtP paths MAs.

Turning now to FIG. 2, there is shown a flow diagram showing steps of anexemplary embodiment. The following numbering corresponds to that ofFIG. 2.

S1. ECMP multipoint paths are generated and are identified by a set ofSPB Group Addresses as described above.

S2. ECMP PtP and multipoint path MAs are determined in order to monitorthe ECMP paths. The ECMP path MAs can be associated with a connectivitypath connecting a specific group of endpoints or with a subset (notnecessarily proper) of equal cost paths connecting the same end points.Each ECMP PtP individual path is identified by a Flow Hash value, whileeach ECMP multipoint individual path is identified by an SPB GroupAddress as described above.

S3. CFM PDUs are sent and processed on those MAs determined in step S2.When multiple paths are used, the corresponding CFM PDUs are sent ingroups cyclically on every monitored path, using the identifierassociated with every monitored path. The number of CFM PDUs in everygroup depends on the specific CFM PDU. For example, for CCMs thereshould be sent at least 4 CCMs on a single monitored path before movingto the next one. For LBMs, as many LBMs as provided by the administratorthat initiated the LBM are sent. For LTMs, only one LTM is sent.

As described above, there are various ways in which I-SID subsets thatdefine paths can be mapped to Group MAC addresses.

Turning now to FIG. 3, there is illustrated a node 5 for use in acommunications network. Examples of implementations of the node 5 areany types of device that implement ECMP. This includes a VLAN awarebridge that implements IS-IS SPB and all the ECMP related functionalityas described by P802.1Qbp. The node 5 may also be implemented in anydevice (virtual or physical), such as a router or a virtual machine,that implements the ECMP related functionality as described inP802.1Qbp.

The node 5 is provided with a processor 6 for generating the ECMP pathsand applying them to data and CFM PDUs. A transmitter 7 and receiver 8may also be provided. Note that this may be in the form of a separatetransmitter and receiver or in the form of a transceiver. Anon-transitory computer readable medium in the form of a memory 9 may beprovided. This may be used to store a program 10 which, when executed bythe processor 6, causes the node 5 to behave as described above. Thememory 9 may also be used to store tables 11, such as Tables 1 to 3described above for mapping I-SID values and Group MAC addresses topaths. Note that the memory 9 may be a single physical memory or may bedistributed or connected remotely to the node 5. In the example of FIG.2, the memory is shown as being located at the node 5.

Note also that the computer program 10 may be provided on a furthernon-transitory computer readable medium 12 such as a Compact Disk orflash drive and transferred from the further memory 12 to the memory 9or executed by the processor 6 directly from the further memory 12.

A node such as a Bridge network node supporting ECMP can typicallysupport a plurality of other service types (such as VLAN, TrafficEngineered services, Backbone tunnel services, etc). In an embodiment,the network is a Provider Backbone network where its edges (theendpoints described above) are Backbone Edge Bridges (which canencapsulate and decapsulate received frames) while transit Bridges arecalled Backbone Core Bridges which do not haveencapsulation/decapsulation capabilities. The network needs to runShortest Path Bridging in MAC mode (SPBM) which is used to createshortest paths between the edges. ECMP further updates SPBM in order toenable multiple paths among the same edges. A node performing ECMPtypically has processing capabilities and requirements associated withthe ECMP service monitoring. That is, ECMP MEPs need to be instantiatedat the BEBs (in particular CBPs (Customer Backbone Ports within theBEBs) in order to initiate and process CFM PDUs associated with the ECMPservices, and ECMP MIPs need to be instantiated at BCBs in order toprocess received CFM PDUs and respond.

Turning to FIG. 4 herein, there is illustrated a vessel or vehicle 13,examples of which include a ship, a train, a truck, a car, an aeroplaneand so on. The vessel/vehicle 13 is provided with the node 5 describedabove.

It will be appreciated by the person of skill in the art that variousmodifications may be made to the above described embodiments. Forexample, the functions of the network node are described as beingembodied at a single node, but it will be appreciated that differentfunctions may be provided at different network nodes.

The following abbreviations have been used in this specification:

BEB Backbone Edge Bridge

B-VID Bridging VLAN Identifier

CBP Customer Backbone Port

CCM Continuity Check Message

CFM Connectivity Fault Management

ECMP Equal Cost Multiple Paths

FDB Filtering Database

IS-IS Intermediate System to Intermediate System

I-SID Backbone Service Identifier

LBM Loopback Message

LTM Link Trace Message

MA Maintenance Association

MEP Maintenance Association Edge Point

OAM Operations, Administration and Maintenance

PBB-TE Provider Backbone Bridges—Traffic Engineering

PDU Protocol Data Unit

PtP Point to point

SPB Shortest Path Bridging

SPBM Shortest Path Bridging—MAC address mode

TESI Traffic Engineered Service Instance

VID VLAN Identifier

VLAN Virtual LAN

What is claimed is:
 1. A method of monitoring a Maintenance Associationfor Connectivity Fault Management in a network supporting Equal CostMultiple Paths, ECMP, the method comprising: generating a set of ECMPpaths for sending data between endpoints in the network; creating a setof ECMP Maintenance Associations for monitoring the generated ECMP pathsbetween the endpoints; and using the created set of ECMP MaintenanceAssociations for sending monitoring packets.
 2. The method according toclaim 1, wherein each monitoring packet comprises a Connectivity FaultManagement Protocol Data Unit.
 3. The method according to claim 1,further comprising generating the set of ECMP paths using ECMP Point toPoint paths, each of the ECMP Point to Point paths comprising a set ofequal shortest length connectivity paths between two endpoints of theECMP Point to Point path.
 4. The method according to claim 1, furthercomprising generating the set of ECMP paths using ECMP multipoint paths,the multipoint paths comprising a set of connectivity multipoint pathsamong the same endpoints.
 5. The method according to claim 4, whereineach ECMP path comprises an ECMP multipoint path having N endpoints, themethod further comprising identifying each ECMP multipoint path using aGroup address.
 6. The method according to claim 4, further comprisingidentifying each ECMP multipoint path associated with the N endpointsusing a Group MAC address.
 7. The method according to claim 6, furthercomprising constructing the Group MAC address by applying an operationon Backbone Service Identifier values associated with the ECMPmultipoint paths.
 8. The method according to claim 1, further comprisingmonitoring an ECMP path by sending the monitored packet using anidentifier associated with the monitored ECMP path.
 9. The methodaccording to claim 8 wherein the identifier is selected from any of aFlow Hash and a Group MAC address identifying the path.
 10. The methodaccording to claim 1, further comprising monitoring a plurality of ECMPpaths by sending monitored packets in groups cyclically on eachmonitored ECMP path, using an identifier associated with each monitoredECM P path.
 11. A node for use in a communications network supportingECMP, the node comprising: a processor for generating a set of ECMP pathMAs for sending data between endpoints; the processor being furtherarranged to create a set of ECMP Maintenance Associations for monitoringthe generated ECMP paths between the endpoints; and a transmitter forsending monitoring packets using the set of generated ECMP paths. 12.The node according to claim 11, further comprising a computer readablemedium in the form of a memory for storing information mapping at leastone Service Identifier to each generated ECMP path.
 13. The nodeaccording to claim 11, wherein the processor is further arranged togenerate the monitoring packets using ECMP Point to Point paths, each ofthe ECMP Point to Point paths comprising a set of equal shortest lengthconnectivity paths between two endpoints of the ECMP Point to Pointpath.
 14. The node according to claim 11, wherein the processor isfurther arranged to generate the monitoring packets using ECMPmultipoint paths comprising a set of connectivity multipoint paths amonga plurality of endpoints.
 15. The node according to claim 14, whereinthe processor is arranged to identify each ECMP multipoint pathmonitoring packet using a Group MAC address for each ECMP multipointpath.
 16. The node according to claim 15 wherein the processor isarranged to construct each Group MAC address by applying an operation onBackbone Service Identifier values associated with the ECMP multipointpaths.
 17. A non-transitory computer readable medium which, when run ona node, causes the node to perform the method of claim
 1. 18. A vesselor vehicle comprising the node as claimed in claim 11.